Photoperiod-related changes in thermoregulatory capacity in gray mouse lemurs (Microcebus Murinus)

Abstract

Seasonal endocrinal changes, such as modulation of insulin-like growth factor 1 (IGF-1) levels, may allow animals to cope with temperature variations. To test this hypothesis, we evaluated the effects of season on thermoregulatory capacities in a photoperiod-responsive species, the gray mouse lemur ( Microcebus murinus ). Adult male mouse lemurs were exposed to ambient temperatures (Tas) of 12, 25, and 34 °C, and we monitored changes in daily rhythms of body temperature (Tb) and IGF-1 blood levels. Additionally, we observed the exploration and choice of Ta in a thermal gradient over 24 h after animals had been acclimated to 25 °C. Under winter-like short photoperiod (SP) exposure, mouse lemurs in the thermal gradient showed marked behavioral adjustments and Tb fluctuations, in response to Ta fluctuations similar to those occurring in the Malagasy winter. In contrast, under summer-like long photoperiod (LP), behavioral responses and Tb changes were only moderate, corresponding to the lower Ta fluctuations observed in summer. Overall, IGF-1 levels remained higher under LP than under SP, whatever the Ta. Thermal challenges evoked different modulations of IGF-1 according to season, e.g., a slight increase under SP and a transient decrease under LP after heat challenge. Altogether, our results indicate that photoperiod exerts a major in fluence on thermoregulatory capacities, with IGF-1 playing an important role in mechanisms of thermogenesis/thermolysis.